The present invention relates to an apparatus and method for controlling fuel injection in an internal combustion engine that includes a plurality of sets of fuel injection valves, each set corresponding to a single cylinder and supplying fuel to a combustion chamber of the corresponding single cylinder.
Conventionally, as an apparatus for controlling fuel injection in an internal combustion engine, the one disclosed in Japanese Laid-Open Patent Publication No. 3-185242 is known. The fuel injection controlling apparatus of the publication includes in-cylinder injectors, each of which directly injects fuel into one of combustion chambers, and port injectors, each of which injects fuel to one of intake ports. According to the operating state of an internal combustion engine, the apparatus switches between an injection mode, in which fuel is supplied to each combustion chamber by using only the in-cylinder injector in the corresponding in-cylinder injector and port injector, and another injection mode, in which fuel is supplied to each combustion chamber by using both of the corresponding in-cylinder injector and port injector.
Further, when performing feedback control to control the actual air-fuel ratio of the internal combustion engine to the stoichiometric air-fuel ratio, the fuel injection controlling apparatus learns an air-fuel ratio learning value to compensate for a steady-state deviation of the actual air-fuel ratio in relation to the stoichiometric air-fuel ratio. Specifically, the apparatus learns the air-fuel ratio learning value separately for the injection mode, in which fuel is supplied to each combustion chamber by using only the in-cylinder injector in the corresponding in-cylinder injector and port injector, and for the other injection mode, in which fuel is supplied to each combustion chamber by using both of the corresponding in-cylinder injector and port injector.
Further, in a case where the fuel injection modes of the fuel injection controlling apparatus include an injection mode, in which fuel is supplied to each combustion chamber by using only the port injector in the corresponding in-cylinder injector and port injector, the apparatus learns the air-fuel ratio learning value for this injection mode separately from the other injection modes.
However, in the injection modes in which fuel is supplied to each combustion chamber by using either one of the corresponding in-cylinder injector and port injector, learning conditions sometimes are not met. In the injection modes, until the learning conditions are met, the fuel injection amount of each injector is not corrected to compensate for the deviation of the actual air-fuel ratio in relation to a target air-fuel ratio. This may degrade the injection control performance.